package dataStructQueue;

import java.util.Stack;

class MyQueue2 {
    // 用两个栈 实现 一个队列

    private Stack<Integer> stack1;
    private Stack<Integer> stack2;

    public MyQueue2() {
        stack1 = new Stack<>();
        stack2 = new Stack<>();
    }
    
    public void push(int x) {
        stack1.push(x);
    }
    
    public int pop() {
        if(empty()){
            return -1;
        }
        if( !stack2.isEmpty()){
            return stack2.pop();
        }else {
            int size = stack1.size();
            for (int i = 0; i < size; i++) {
                stack2.push(stack1.pop());
            }
            return stack2.pop();
        }
    }
    
    public int peek() {
        if(empty()){
            return -1;
        }
        if( !stack2.isEmpty()){
            return stack2.peek();
        }else {
            int size = stack1.size();
            for (int i = 0; i < size; i++) {
                stack2.push(stack1.pop());
            }
            return stack2.peek();
        }
    }
    
    public boolean empty() {
        return stack1.isEmpty() && stack2.isEmpty();
    }
}